I am trying to understand my garden's microclimates.
I've read that cold air drains down slopes and accumulates in pockets at the bottom. But I have also read that protected areas adjacent to brick walls can be much warmer that the other areas.
I would like to find the best spot to plant a heat-loving tree. Can you please help me sort this out? This is a picture of my garden, looking NE.
Thanks for any clarification!
Roberta
I posted something on your thread in the California forum, but I'll post here too in case it might benefit someone else. It is true that cold air does tend to drain downward, but there are many other factors that come into play as well--what obstacles are there (houses, trees, etc), where the wind is coming from, etc. The warmest microclimate in my yard is actually at the bottom of one of my hills up against the house, which is where cold air ought to accumulate. It's an east facing wall that doesn't get a lot of sun, so the wall radiating heat is not a significant factor, although heat from the house undoubtedly does help out a little. On the other side of the house, I have a west facing wall that does get a lot of sun and things that are right up next to it tend to be OK (although the area's still not as warm as the area on the other side of the house), but you get a little ways out from the house, even before the land starts to slope down again, you'll find the coldest microclimate in my yard and the place things are most likely to get frost damage in the winter is there. The second coldest microclimate is at the top of my front yard hill. If you strictly looked at the air flow and where cold air ought to end up, those areas at the top of the hills should be the warmest rather than the coldest microclimates.
If you're just looking for summer heat though and trying to push the winter hardiness isn't an issue then it's a little bit easier. Assuming you don't have trees or a building shading the area, places on the south and west side of the house will tend to always be a bit warmer than the north and east sides. My west facing backyard bakes in the afternoon sun, while my east facing front yard is much cooler since the sun's only on it during the morning hours. If you've got a brick wall around and it's on one of those hotter sides of your house then that can provide a little extra heat, but if you're trying to grow a heat loving tree unless it's a really tall wall I think the tree will quickly become too tall for the wall to offer any benefit. Lower growing plants though it could be beneficial. But if the wall is on the north or east side, then I think you'll get more heat for your plants by ignoring the wall and planting your plants on the south or west sides of the house.
Ecrane, how come I didn't think of this before!!? Of course the tree will be taller than the wall! There are things that are so simple it takes a second set of eyes to see! That low wall is west facing though, which is good. And yes, I am thinking about pushing winter hardiness, I love tropical plants, and I am wondering how far I can go in pushing hardiness along that wall.
Now another dumb question, you might not know the answer but I'm throwing it out there. Which colors would enhance the radiating heat effect, dark colors or light colors? Light ones are supposed to radiate heat, and dark ones to hold it, but what does it mean for the area around the wall?.....
Light colored walls would be better if you're trying to maximize summer heat (people who live in cool summer climates and try to grow heat/sun loving plants can benefit by mulching with white rocks, or planting in front of a white wall, etc). But since the white reflects the light, it's going to be most helpful during the day when the sun's shining, and for winter protection you need heat after the sun goes down, so I suspect a dark wall will probably provide more benefit since it will absorb heat during the day and then will cool down slowly overnight. However, if this is just a low wall, then factors like the air flow and wind could very well outweigh the benefit that the wall provides, so I think you're going to have to treat the first winter as an experiment--I'd find a cheap plant that is somewhat borderline in your zone and plant several at different places in your yard and see which ones do best, then you'll know which areas are better microclimates.
Great idea! Also, do you think that little hill behind the wall also keeps the warmth or not? It pretty much gets sun all day long (it's west facing)...I think I need to find out where the wind goes, but I definitely never felt any wind coming down the slope.
I think the darker color would be my best bet from what you say. It's hot enough during the day!!!
If you only pay attention to where cold air ought to go, the bottom of a hill is going to be where cold air collects, so that might not be the best place. Of course as I said with my yard, none of my microclimates work out the way you would predict based on just where cold air should tend to collect, but I'd definitely do some experiments this winter before you decide that's the right place for your tropicals or not. The effect of the wall is all about thermal mass, and if the wall is small it may hold some heat but it'll dissipate pretty quickly as the night gets cooler. So by the time you get to the coldest part of the night there may be no heat left from it, and if cold air is collecting at the bottom of the hill, then you could wind up with problems. If it's a large wall though it may help out a lot. I wish I could tell you how to predict ahead of time where your good microclimates are going to be, but really the only way you're going to find them is either to remember where you've seen the most frost or the most damage in previous years, or plant some similar plants in a variety of places in your yard and pay attention this winter.
